A reaction runs in an insulated container open to the atmosphere, so all heat exchange happens at constant pressure. The heat flow measured for this process equals which quantity?

Core Concept

At constant pressure the heat flow for a process is defined as the enthalpy change, qp = ΔH. This identity is why coffee-cup calorimetry delivers ΔH values directly. Constant-volume devices such as bomb calorimeters instead track the internal energy change ΔE. Activation energy and entropy change are different quantities that a heat measurement alone cannot supply.